1. Technical Field
The present invention relates to polyester fibers or filaments having improved properties in dyeability, deep color dyeability and lightfastness. The present invention further relates to composite fibers comprising the polyester constituting the above polyester fibers as a component, mixed filament yarns with differently shrinkable filaments or sheath-core textured yarns comprising the above polyester filaments as a component, and blended spun yarns comprising the above polyester staple fibers as a component.
2. Background Art
Polyester fibers represented by polyethylene terephthalate fibers have been used in a wide range of applications because of their superior characteristics. However, the fibers have disadvantages in color brightness, color depth particularly in deep black tone, and color development as compared to natural fibers, such as wool and silk, and semi-synthetic fibers such as rayon and acetate fibers.
These disadvantages are caused, generally, by the fact that polyester fibers are dyed with disperse dyes which tend to give an insufficient brightness to the dyed articles, and that polyester fibers have a higher refractive index in a direction perpendicular to the fiber axis of 1.7 as compared to other fibers, which increases light reflectivity on the fiber surface, thereby increasing the intensity of white light reelection and scattering from the surface of fabrics comprising polyester fibers.
To improve these disadvantages, many proposals for introducing dyeable sites for bright color dyes such as cationic dyes and acidic dyes into polyester fibers have been offered. These modifications have improved the dyed fabrics in color brightness, but achieved no substantial success in reducing the white light reflection and scattering and in improving color depth due to the high refractive index of the fibers.
Japanese Patent Publication No. 42938/1992 proposes covering the surface of polyester fibers with a compound having a low refractive index, to achieve deep color dyeability. The publication mentions as examples of this type of compound organic fluorine and organosilicon compounds.
Japanese Patent Publication Nos. 20304/1987 and 28229/1987 propose a method which comprises forming, on the surface of polyester fibers, fine projections and recesses having a pitch smaller than light wave length, thereby suppressing reflection and scattering of light on the fiber surface.
However, with the fibers covered with a low refractive index compound, the covering film has poor durability against dry cleaning. Besides, the covered fibers, if they have achieved a sufficient deep color dyeability at all, give dyed articles having the new drawbacks of poor hand, colorfastness and lightfastness.
The fibers with a very minutely toughened surface obtained by the above method suffer a damage to the toughened surface during post-processing, which reduces the effect of suppressing reflection and scattering of light on the fiber surface. Besides, fabrics made from this type of fibers tend to have a poor appearance due to wear when they are worn.
One of the modifications of polyester fibers is highly shrinkable fibers, which are used for the following applications: (1) they are combined with less shrinkable fibers, and fabrics made therefrom are heat treated to achieve a bulky hand created by the difference in the fiber length; (2) the highly shrinkable fibers with a large fineness are combined with less shrinkable fibers with a small fineness, and fabrics made therefrom are heat treated to produce fiber length difference, whereby the fine fibers positioned on the fabric surface produce a gentle surface touch and the coarse fibers positioned in the fabric core produces good HARI (anti-drape stiffness) and KOSHI (stiffness); (3) the highly shrinkable fibers are used as ground yarns of pile knit or pile fabrics, thereby increasing the density of loops or fluffs; (4) a highly shrinkable polymer is used as a component of composite fibers, which will become latent crimpable fibers; and (5) the highly shrinkable fibers are used upon integral molding and three-dimensional molding.
The highly shrinkable fibers have been prepared by modifying, upon polymerization for the raw material polyester, its acid component by polymerizing isophthalic acid with terephthalic acid. This is considered to be because that this process of modifying the acid component is most advantageous in conducting separation and recovery of ethylene glycol component in the polymerization process. However, this acid component modifying process, requiring a high copolymerization ratio, has the disadvantage of deteriorating superior characteristics inherent to polyester.
Such being the case, not only the modification of acid component but also that of glycol component has been practiced in recent years. Among products obtained by the above processes, most common polyesters are those copolymerized with an alkylene oxide adduct of bisphenol A and those copolymerized with isophthalic acid and an alkylene oxide adduct of bisphenol A. These polyesters exhibit higher shrinkability with smaller copolymerization ratio as compared to those with modified acid component alone. Accordingly, this method is effective in obtaining high shrinkability and high shrinking stress while maintaining good properties inherent to polyester.
However, polyesters copolymerized with an alkylene oxide adduct of bisphenol A have the disadvantages of very poor lightfastness and colorfastness.
Another method for obtaining highly shrinkable polyester fibers comprises heat drawing polyester fibers at a low temperature, thereby decreasing the degree of crystallization of the polyester. This method can surely produce highly shrinkable polyester fibers, which, however, have low heat shrinking stress because of reduction in stress during dry heating. Consequently, the highly shrinkable effect cannot be exhibited in woven or knit fabrics utilizing mixed filament yarns combining less shrinkable fibers with such highly shrinkable fibers.
The present inventors have made an intensive study to obtain a fiber having excellent dyeability and deep color dyeability, as well as high shrinkability and shrinking stress. As a result, it was found that polyesters copolymerized with a compound having a specific chemical structure in a specific amount can provide fibers having sufficient dyeability, deep color dyeability and shrinking characteristics.
Polyesters copolymerized with the compound with the specific chemical structure in an amount of 50-100 mole % are disclosed in U.S. DEFENSIVE PUBLICATION T896033, but the polyester have been difficult to convert into fibers.
The present invention is based on the finding that copolyesters polymerized with the compound with a specific chemical structure in a specific amount are convertible into fibers, which have not only sufficient dyeability, deep color dyeability, high shrinkability and shrinking stress characteristics, but also superior lightfastness and colorfastness.
It is an object of the present invention to provide a polyester fiber or filament having not only excellent dyeability, deep color dyeability, high shrinkability and shrinking stress characteristics, but also excellent lightfastness and colorfastness.
Another object of the present invention is to provide a mixed filament yarn or sheath-core textured yarn comprising this polyester filament.
A further object of the present invention is to provide a blended spun yarn comprising as one component staple fibers comprising a polyester constituting the above polyester fiber.
A still further object of the present invention is to provide a composite fiber comprising as a component the polyester constituting the above polyester fiber.